SBPAT

Mean effluent concentrations of stormwater BMPs reported in the International BMP database are used to estimate BMP performance in SBPAT. While SBPAT is capable of simulating many different types of BMPs, performance data is not available for all types currently included. If the unit treatment process for a BMP with data can be expected to be similar for a BMP without data, then equivalent performance is assumed. However, if no data exists and treatment processes cannot be associated with a BMP with data, then only load reductions associated with simulated volume loss are assumed.

The model package comes with geospatial drainage area information specific to LA County or Orange County, which the user is directed to save locally and identify the file path as a model input. Once the geospatial database or geodatabase for the desired watershed is pre-processed, the user is required to select distributed and regional scale BMPs to evaluate by catchment (for both regional and distributed scale BMPs) and land use treated (for distribute BMPs only). To use geospatial drainage area data that is updated or for a different region, the user must refer to the SBPAT User Guide and Database Guide Appendix (Appendix D) to ensure that alternate datasets have the required fields and formats for use in SBPAT’s preprocessing step.

Output is in the form of a text file or formatted Microsoft Excel reports. The text file provides detailed model results, including estimates of uncertainty in terms of standard deviations and confidence intervals. The formatted reports summarize average annual reductions in runoff volumes, loads, and concentrations associated with BMP implementation. The three report summaries include average annual volume and load summary, storm event concentrations summary, and BMP cost summary. SBPAT results will present loads, volumes, and storm event concentrations under three scenarios: pre-BMP, with distributed BMPs, and with regional and distributed BMPs.

• Tool may be used during the planning phase of stormwater program
• SBPAT is a complex statistically-driven (stochastic) stormwater model
• Model comes with either LA County or Orange County data preprocessed (depending on SBPAT version)
• Requires ArcGIS 10. Spatial Analyst extension required for data preprocessing in areas outside of the LA County and Orange County
• This tool is not recommended for catchments over a few hundred acres in size
• The tool is intended for comparing catchments to prioritize BMP implementation, not to provide precise pollutant load reduction estimates
• The model addressed stormwater pollutant loading by land use
• Receiving water modeling addressing point source or dry weather flows and loads is not possible with this tool
• This tool is free and available to the public

• This tool has ability to estimate planning level capital and operation and maintenance costs for implementing BMPs
• This tool is capable of comparing opportunities in multiple catchments and prioritizing implementation based on water quality improvement need and highest potential for implementing structural BMPs
• This tool may be used to support Reasonable Assurance Analysis (RAA)